1. Field of the Invention
The present invention relates to a method for producing carbon nanocoils, and more particularly relates to a method comprising: providing catalyst on the metal substrate, and growing carbon nanocoils efficiently from the catalyst surface under the atmosphere of a carbon-based gas.
2. Description of Related Art
A carbon nanocoil is a hollow tubule presented in a helical shape and constituted from carbon atoms. In 1953, Davis et al. proposed the discovery of a helical shape appearing in some carbon tubules, wherein the diameter of such helical-shaped carbon tubules was at micro-level and so were called vermicular threads (Nature vol. 171, p 756). Afterwards, some studies were directed to those carbon micro-coils. However, such carbon micro-coils are difficult to manufacture for the commercial use because the repeatability of the producing of the carbon micro-coils is very low.
In the 1990s, Motojima et al. developed a method of effectively fabricating a great quantity of micro-carbon coils, and the repeatability is high (App. Phys. Lett. Vol. 56, p 321). In such method, nickel as a catalyst is plated on graphite used as a base, and the base is then placed in a quartz tube (which is known as a reaction carrier), followed by heating in a quartz tube furnace at 750° C.-800° C. with the adding of acetylene, hydrogen, nitrogen, and divinylene sulfide to grow micro-carbon coils.
In 1994, carbon coils having diameter of nano-sized were developed by Amelinckx et al. (Science vol. 265, p 635). These carbon nanocoils are well-graphitized and extremely thin coiled nanotubules (the coil diameter of the smallest one is about 12 nm). They are produced by using metal particles, such as iron, cobalt, and nickel, as catalyst, heated to about 600° C. to 700° C., and induced with the mixture of acetylene and benzene to grow carbon nanocoils. However, the output quantity and the yield of the carbon nanocoil is not ideal, sometimes accompanied with some undesired straight carbon tubules.
In 1999, carbon coils having diameter of nano-sized were developed by Li et al. (J. Material Sci. vol. 34, p 2745). These carbon nanocoils are prepared by covering a graphite sheet with iron particles (granule, whereafter the catalyst was heated to 700° C., and a mixture of acetylene and nitrogen (1:9) was supplied at the rate of 1000 sccm to perform growth. However, the yield of the carbon nanocoil was still disappointingly low, and such method cannot be applied to large quantity manufacture for commercial use.
In 2005, Nakayama et al. (J. Phys. Chem. B 109, 17366) used Fe—In—Sn—O fine particles as catalysts depositing on a substrate for synthesizing carbon nanocoils by catalytic thermal chemical vapor deposition. The carbon nanocoils were produced as follows. Iron chloride (FeCl3), indium chloride (InCl3), and tin chloride (SnCl3) were first dissolved in deionized water with the same concentration, and then these solutions were mixed with appropriate ratios. An alkaline solution, i.e. an aqueous solution of ammonium carbonate ((NH4)2-CO3), was added to this ion solution to precipitate hydroxides of iron, indium, and tin. The hydroxides were dried on a substrate surface, and heated under 600° C. for 2 hours to perform metal hydroxide catalysts. Fine particle catalysts were put in the quartz tube reactor and then heated to 700° C. in a helium (He) atmosphere at the rate of 200 sccm. After heating to 700° C., acetylene gas was supplied at the rate of 60 sccm for 30 min to perform catalytic thermal chemical vapor deposition. However, the substrates used in the above methods were usually made of graphite or silicon wafer, which are expensive and limited to small size and inconsistent shape, thus the cost is always high and it is difficult for large quantities to be manufactured.
Although the yield is higher by using oxides of Fe—In—Sn as catalysts to provide carbon nanocoils, it is inconvenient for the preparation of the raw materials because the kinds of the raw materials are complex, and the process cannot proceed if there is any one of the raw materials absent. Consequently, the method of the prior art is difficult for large quantity production.
As a result, it is a present need to develop a novel method of providing carbon nanocoils with low cost and large quantity production.